Heretofore, it has been known to use plastic knuckle pins in couplers on railway cars, as disclosed in U.S. Pat. No. 5,145,076, the disclosure of which is incorporated by reference. The known plastic knuckle pins of the type shown in the patent are made from a self-lubricating plastic material exhibiting sufficient flexibility to absorb substantial bending stresses without breaking, thereby enhancing the life of the pins. While it is suggested in the above patent that the plastic knuckle pin may be hollow or made in more than one piece, it is disclosed to be preferably molded as a unitary solid piece. Plastic knuckle pins have been proven superior over steel knuckle pins because the plastic knuckle pin absorbs substantial bending stresses without breaking and therefore enjoys a longer life. Moreover, plastic knuckle pins are substantially lighter in weight and therefore easier to handle.
However, it has been found that the injection molding process used to form the known solid plastic knuckle pin creates some, if not a multitude of, liberties or trapped air pockets in the plastic pin. Further, if the solid plastic pin is made during humid weather, the plastic material tends to absorb moisture from the air during molding. Both of these phenomena result in a plastic knuckle pin having less than an optimal material matrix uniformity. It is therefore desirable to produce a solid plastic knuckle pin characterized by a substantially higher material matrix uniformity than the current known solid plastic knuckle pins.